DESCRIPTION (Applicant's abstract): The ability to treat discriminatively different external stimuli as members of a common class is the defining attribute of conceptualization. Prior work has shown that animals as diverse as human beings and pigeons can classify lifelike visual stimuli into natural and artificial categories. The present competitive continuation application aims to see whether the perceptual processes of conceptualization are similar in humans and pigeons. Pigeons will be trained with operant conditioning procedures to discriminate line drawings and computer renderings of natural and artificial stimuli. The pigeons will then be tested with specially modified stimuli that: (1) remove certain portions of the training stimuli, (2) rearrange its component parts, (3) rotate the image in depth. These test stimuli produce highly specific effects in humans, which encourage the view that human object recognition is mediated by a structural description specifying a non-accidental (i.e., viewpoint-invariant) representation of the parts and the relations among those parts--recognition by components. If people and pigeons similarly process visual stimuli, then the results of the planned series of experiments with pigeons should parallel those with people. Empirical convergence would attest to the economy of nature and to the superfluity of language for conceptualization. Empirical divergence would imply that different neurobiological or linguistic mechanisms mediate visual concepts in people and pigeons. In either case, the results of this research project should shed considerable light on the species generality of conceptualization and could yield important clues for how cognitive and computer scientists might more successfully design intelligent systems that are capable of visual pattern recognition. The results could also promote the behavioral analysis of discrimination and generalization processes in learning-disabled or language-deficient humans.